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Production and preservation ofhigh quality forages has long been a concern for producers. This publication is jointly sponsored by the Crop Science Society ofAmerica and American Society ofAgronomy. It represents the most current knowledge about preservation offorage crop quality as it is influenced by postharvest physiology and microbiology. Producers, agronomists, and crop scientists will fmd the information in this publication to be beneficial and useful, particularly as it relates to field curing offorages, and hay and silage preservation.
Post-Harvest Physiology and Preservation of Forages Related Society Publications Forage Cell Wall Structure and Digestibility Forage Quality, Evaluation, and Utilization For more information on these titles, please contact the SSSA Headquarters Office; Attn: Marketing; 677 South Segoe Road; Madison, WI 53 711-1086 Phone: (608) 273-8080, ext 322 Fax: (608) 273-2021 Post-Harvest Physiology and Preservation of Forages Proceedings of a symposium sponsored by C-6 of the Crop Science Society of America The papers were presented during the annual meetings in Minneapolis, MN, 1-6 Nov 1992 Co-Editors Kenneth J Moore Michael A Peterson Managing Editor David M Kral Managing Editor Marian K Viney CSSA Special Publication 22 American Society of Agronomy, Inc Crop Science Society of America, Inc Madison, Wisconsin, USA 1995 iii Copyright© 1995 by the American Society of Agronomy, Inc Crop Science Society of America, Inc Soil Science Society of America, Inc ALL RIGHTS RESERVED UNDER THE U.S COPYRIGHT ACT OF 1976 (P.L 94-553) Any and all uses beyond the limitations of the "fair use" provision of the law require written permission from the publisher(s) and/or the author(s); not applicable to contributions prepared by officers or employees of the U.S Government as part of their official duties American Society of Agronomy, Inc Crop Science Society of America, Inc Soil Science Society of America, Inc 677 South Segoe Road, Madison, WI 53711 USA Library of Congress Cataloging-in-Publication Data Post-harvest physiology and preservation of forages : proceedings of a symposium sponsored by C-6 of the Crop Science Society of America I co-editors, Kenneth J Moore, Michael A Peterson [et al.] p em - (CSSA special publication : 22) "The Papers were presented during the annual meetings in Minneapolis, MN, 1-6 Nov 1992." Includes bibliographical references ISBN 0-89118-539-9 Forage plants-Postharvet physiology-Congresses Forage plants-Postharvest technology-Congresses I Moore, Kenneth J II Peterson, Michael A III Crop Science Society of America Division C-6 IV Series : CSSA special publication : no 22 SB188.P7 1995 633.2'086-dc20 95-6087 CIP Printed in the United States of America iv CONTENTS Page Foreword Preface Contributors vii ix xi Post-Harvest Physiological Changes in Forage Plants Lowell E Moser Microbiology of Stored Forages Craig A Roberts 21 Field Curing of Forages C Alan Rotz 39 Hay Preservation Effects on Yield and Quality Michael Collins 67 Legume and Grass Silage Preservation E.H Jaster 91 v Foreword Production and preservation of high quality forages has long been a concern for producers This publication is jointly sponsored by the Crop Science Society of America and American Society of Agronomy It represents the most current knowledge about preservation of forage crop quality as it is influenced by post-harvest physiology and microbiology Producers, agronomists, and crop scientists will fmd the information in this publication to be beneficial and useful, particularly as it relates to field curing of forages, and hay and silage preservation The co-editors of Post-Harvest Physiology and Preservation of Forages, K.J Moore and M.A Peterson, are well-recognized for their contributions to the current state ofknowledge in this area of forage research The authors, M Collins, E.H Jaster, L.E Moser, C.A Roberts, and C.A Rotz are leading scientists and educators in their respective disciplines Their background and expertise are wellsuited to integrate the most current knowledge on the complex subject of forage crop preservation This publication will serve as a technical reference for teachers, researchers and producers, who are interested in forage quality and utilization It will be helpful in identifying, understanding and managing factors associated with forage crop losses in quality and quantity from the time of harvest through the time of its use The technical content of this reference should beneficial for years to come Robert (Bob) C Shearman President, CSSA vii Preface The preservation of forage crops is one of the most risk-intensive processes undertaken by farm managers From the time that a forage crop is first cut until it is used as feed, it is subject to significant losses in quality and quantity These losses are incurred through a complex set of biotic and abiotic processes that occur during harvesting and field operations, and later during storage and handling of the product To minimize the risk associated with forage preservation it is important to understand these processes, how they interact with one another, and how their effects can be mitigated through various management practices This special publication is based on a symposium of the same title that was sponsored by the Crop Science Society of America and held during the 1992 annual meeting in Minneapolis, MN The objective of the symposium was to integrate knowledge from several disciplines as it relates to the preservation of forage crops This publication brings together for the frrst time in one document the current level of knowledge in this important area It is intended to be useful to a broad audience ranging from forage producers to scientists working in the general area of forage quality and utilization The editors wish to express their gratitude to the symposium planning committee who developed the original outline for this publication and to the authors for their efforts in the preparation of the chapters Kenneth J Moore Iowa State University, Ames, Iowa Michael A Peterson W-L Research, Inc., Evansville, Wisconsin ix 102 JASTER inoculated com silage; no response was observed in wheat and alfalfa silages Petit and Flipot ( 1990) observed no beneficial effect of adding a microbial inoculant mixture on silage composition; however, intake of silage constituents was higher for inoculated than for noninoculated silages, possibly improving animal performance Preservation and digestibility were enhanced in wheat silage grown under normal rainfall and environmental temperatures and depressed in drought-stressed wheat forage inoculated with a mixture of Streptococcus faecium, L plantarum, and Pediococcus acidilacti (2 x 109 g-1) Microbial-inoculated silage resulted in increased DM and fiber digestibility of wheat silage based rations fed to Holstein heifers (Froetschel et al., 1991); however, inoculants provided no advantage in many research trials Ely et al (1982) evaluated the addition of Lactobacillus acidophilus and Candida sp (5 g kg-1) to fresh forage in stored concrete stave silos Data showed no advantage of L acidophilus and Candida sp to crops at ensiling Absence of any beneficial effect of inoculation on silage pH may be due to DM content of the silages Kung et al (1984, 1987) added inocula to alfalfa wilted to 30, 40, 50, and 60% DM Microbial additions to alfalfa resulted in increased lactic acid at all DM contents, but fmal pH was lower than noninoculated silage only at 50 and 60% DM Shockey et al (1985, 1988) evaluated the inoculation of alfalfa with a mixed inoculum (10 g-1) ofhomofermentative lactic acid bacteria The addition ofLAB had no influence on any chemical or microbiological parameter The relationship between the effect of inoculation with LAB and addition of water soluble carbohydrate (sugar) to forage is controversial Ohyama et al ( 1973) studied the effect of inoculating forage grass with Lactobacillus plantarum (106 g-1), with and without addition of glucose (10 g kg-1), but no beneficial effects of inoculation treatment were detected In subsequent work, Ohyama et al (l975b) reported the effect of inoculating Italian ryegrass and cocksfoot (Dacty/is glomera/a L.) with Lactobacillus plantarum (106 g-1) with or without the addition of glucose (2%) Glucose treatment resulted in large amounts of lactic acid Changes in pH values and volatile basic N levels confirmed the positive effect of glucose addition and L plantarum inoculation before ensiling Seale et al ( 1986) compared the effect of sugar and inoculant addition on fermentation of alfalfa silage They showed that with insufficient sugar in the original crop, bacteria in an inoculant would be unable to produce enough lactic acid to lower pH to an acceptable level Jones et al (1992) ensiled alfalfa treated with sugar (2% fresh weight) and/ or with mixed culture of L plantarum, S faecium, and Pediococcus acidilactici (3 x 10s g-1 herbage), then examined the fermentation characteristics after 60 d of fermentation (Table 5-5) They indicated that silages were well preserved with inoculation increasing the rate of pH decline for all silage dry matters Inoculation and sugar addition lowered fmal pH, acetic acid, ammonia-N, free amino acids, and soluble nonprotein N in silages The combined treatment also increased lactic acid content with 33 and 43% dry matter silages The potential nutritional benefit from reducing proteolysis during ensiling requires further investigation LEGUME AND GRASS SILAGE PRESERVATION 103 Table 5-5 Composition of alfalfa silage treated with inoculant and/or sugar (Jones et al., 1992) Rate of Acetic Lactic pH decline pH Peptide· N Ammonia· N Acid Acid d -I g kg-! -g kg- Total Ng kg- DM 330 0.85 4.38 100 64 21.4 89.4 0.93 330 4.17 142 55 17.8 104.4 330 2.31 4.22 148 42 11.6 99.5 Sugar 330 1.97 4.05 156 33 8.1 109.5 DM Control Sugar Inoculated Inoculated + Reports conducted by other researchers have shown the benefits of including sugars and/or a combination of cell wall degrading enzymes that would increase the fermentation capacity by releasing additional fermentable substrate from cell walls or cell solubles (Woolford, 1984; Herm et al., 1988; Muck, 1988; Kung et al., 1990, 199lb; McDonald, 1991) Cell Wall Degrading Enzymes Addition of cellulolytic and hemicellulolytic enzymes as silage additives has been investigated as a method of increasing fermentable sugars (water soluble carbohydrate) and improving the digestibility of organic matter (Leatherwood et al., 1959; Olson & Voelker, 1961; Owen, 1962; McCullough, 1964, 1970; Autrey et al., 1975; Henderson & McDonald, 1977; Buchanan-Smith & Yao, 1981; Henderson et al., 1982; McHan, 1986; Jaster & Moore, 1988) The process of ensiling is known to effect hydrolysis of structural carbohydrates, especially hemicellulose Morrison (1979) reported losses of I to 20% of the hemicellulose fraction during ensiling of grasses During the experiment, losses of cellulose were 60% (Carpentero et al., 1979) Wilting may require only a few hours if good drying conditions exist, or several days under adverse conditions Crushing or crimping (conditioning) freshly cut forage is normally done to speed up drying Conditioning breaks the waxy surface of stems and creates more cut ends allowing them to dry at a rate more equal to leaves LEGUME AND GRASS SILAGE PRESERVATION 107 Silage produced by the wilting method still depends on lactic acid produced for preservation; however, there is less fermentation than in direct-cut material Therefore, a pH of z4.5 is typical of a wilted silage (Noller & Thomas, 1985) Low moisture silages have a reduced moisture (40-60%) content and limited bacterial growth and fermentation Low moisture silages (also termed haylages) have the advantage of improved DM intake by cattle, reduced fermentation odors, and storage and mechanical feeding equipment available for all silage feeding program Silages with relatively low moisture are best preserved in sealed, 2-limiting silos In some cases, conventional upright silos are used for low moisture haylage, but particular attention must be given to maintaining air-free conditions The important factors are fine chopping, rapid filling, good sealing, and reduced infiltration of air in silo Therefore, bunkers, stacks, trench silos, and bag silos are not frequently used at these moisture contents because of the difficulty in maintaining air-tight conditions Allowing air into haylage will cause heating and the growth of nondesirable yeasts and molds A disadvantage of lowmoisture silage is that it often becomes too dry for good harvesting and storage Harvest losses increase when the forage is drier, and poor packing and retention of air may result in excessive heat damage of the silage A report by Goering and Adams (1973) indicated that z30% of hay crop silages submitted to state laboratories were heat-damaged STORAGE METHODS AND SILOS Forage characteristics and the type of silo affect silage preservation and storage The size and type of silo chosen should be influenced by the number and kinds of cattle to be fed, the quantity of the product to be fed, and dry matter losses occurring during storage (Noller & Thomas, 1985) The sources of these losses are initial aerobic losses due to air entrapped in the forage, fermentation losses primarily from the production of C02 by anaerobic bacteria, effluent losses, long-term storage losses due to air leaks into the silo and the consequent respiration by plant enzyme or aerobic microorganisms (Pitt, 1986) There are a wide variety of silos in use: (i) conventional upright (tower) silos (concrete stave, galvanized steel, wood stave, monolithic, tile block, and brick); (ii) gas tight (0 2-limiting) silos (glass lined structures, concrete stave, galvanized steel, and monolithic concrete); (iii) pit silos; (iv) horizontal silos (trench and bunker silos); and (v) temporary silos including enclosed stack silos, open stack silos, modified trench-stack silos, and plastic silos Estimates of the effect of moisture content of forage to be ensiled on the DM losses in the field and in storage are presented in Table 5-8 Conventional upright (tower) silos are cylindrical in shape and built aboveground The round shape withstands the pressure of forage against the inner walls The silo walls need to be smooth and airtight to minimize surface exposure of air to forage Tower silos are adapted to good packing and should have tight fitting doors Doors may be sealed with building paper or plastic sheeting to prevent air leaks Packing and spreading within the silo is effected by a horizontal rotating plate or nozzle Acid corrosion of JASTER 108 Table 5-8 Estimate of typical dry matter losses in forage stored as silage at different moisture levels based on six months of storage (Shepherd et al., 1953; Moser, 1990) Silo type/Moisture content of forage as stored From cutting Total of crop to Field silo Surface Fermenfeeding spoilage tation Seepage losses lossest % Conventional tower silos 65 g kg- Gas-tight tower silos 65 g kg- 50 g kg- Trench silos 85 g kg- 75 g kg- 70 g kg- Stack silos 85 g kg- 75 g kg- 70 g kg- 12 16 0 0 4 10 10 14 10 11 10 10 27 18 21 2 29 20 23 12 16 20 12 11 12 10 34 30 33 2 36 32 35 t Losses from forage harvester alone walls during fermentation of silages can be reduced with cement resurfacing The primary advantages of tower silos are durability of structure, minimum top and side spoilage, and convenience of feeding during inclement weather Upright silos are well adapted to mechanization with mechanical unloaders located at the top or bottom of the silo Bottom unloaders have the advantage of eliminating silo doors Tower silos vary in size from to diam and up to 24+ m high Forage is best stored between 40 and 80% moisture Relatively high moisture forages (>70%) increase the outward pressure in silo walls and increase the losses of nutrients in effluent (Pitt & Parlange, 1987) Effluent contains high concentrations of water soluble carbohydrates and nitrogenous compounds (McDonald et al., 1960) Oxygen-limiting silos are tower structures sealed by airtight hatches after filling Silos operate on a continuous flow principal and have a shell, limiting access of to silage (Meiering, 1982) The quality of silage in gastight silos is depends on maintaining anaerobic conditions in the head space (Jiang et al., 1989) Advantages include no visible top spoilage, ability to refill at any time, lowmoisture material (40-50%) can be ensiled, no silo chute to climb, bottom unloading, and reduced risk of being exposed to lethal silo gas Some disadvantages are greater cost of construction, slower unloading times than conventional tower silos, and relatively high maintenance costs of 2-limiting silo unloaders Gas exchange between the silo head space in 2-limiting silos and the environment is a result of the pressure fluctuations in the head space The dome of sealed silos contains a gas space that forms after settling of the ensiled crop and increases with unloading Pressure fluctuations are affected by temperature change of the gases in head space or the unloading rate (Meiering, 1986) Breather bags and a pressure relief value are used to reduce the air exchange due to diurnal fluctuations in pressure Wilted forage is usually stored at 45 to 55% moisture to facilitate unloading from the bottom On the average, storage losses are lowest in LEGUME AND GRASS SILAGE PRESERVATION 109 these structures because they are the most air tight; however, initial and annual costs are higher than other types of silos Horizontal trench silos are constructed from excavated soil with one end at ground level to permit good drainage and use of machinery Trench silos are suitable as temporary storage and may be earthen in construction or fmished with a concrete floor and side walls Bunker silos are constructed aboveground using a concrete floor and wooden or concrete airtight side walls In comparison to tower silos, bunker silos have the advantages of low initial cost, ease of construction, rapid filling and packing by machinery, particularly for storage of large amounts of forage for large dairy herds Disadvantages of bunker silos are a greater surface area exposed to air, difficulties in packing and air exclusion (especially when drier forage such as haylage is ensiled), and the inconvenience of feeding in inclement weather Bunker silos need to be sealed airtight to avoid larger losses from silage spoilage (Buckmaster et al., 1989; Parsons, 1991 ) Plastic sheeting properly weighted down, (commonly with used tires) is superior to limestone, soil, poor quality roughage, sawdust, or water proof paper as a protective sealer (Gordon, 1967) Plastic covers keep out rain and snow and exclude air from the surface, lowering ensiling temperatures, pH, lactic acid, and nonprotein N concentrations compared with uncovered bunkers (McGuffey & Owens, 1979; Oelberg et al., 1983) Temporary aboveground bunker silos have been constructed using an earthen floor and round bales of hay or straw to form temporary perimeter walls Greater spoilage of silage would be expected with this system as compared with conventional horizontal bunkers because of greater evaporation and exposure of silage to air Ideally, spoilage in bunker silos should not exceed the top 10 em, out of a m deep mass of silage (=3% spoilage) Temporary silos include enclosed stack silos, open stack silos, modified trench-stack silos, and plastic silos In comparison to tower silos, temporary silos have the advantages of low cost, rapid filling and packing, and convenience of location Stack silos usually are comprised of a pile of forage built vertically aboveground Surfaces of silage may be left exposed to air or enclosed with straight sides of snow or picket fence, poles or wood staves, and woven wire The top of stack is either left exposed to air or covered with plastic weighted down by used tires The amount of spoilage varies from 10 to 50 em on top and sides of the silage stack Usually the walls of stack silos are weak and height of the stack should not be greater than twice its diameter As much as 35% spoilage may occur in stack silos because of the large surface area exposed (Hight & George, 1983); however, with proper packing and sealing silage fermentation losses in stack silos may range from 10 to 14% (Savoie et al 1986; Savoie, 1988) Temporary silos constructed of heavy plastic and formed in the shape of a tube have been used successfully in forage feeding programs (Rony et al., 1984) Forage is forced into a plastic sleeve with one end closed, and extension of the sleeve is resisted by a retaining mesh, controlled hydraulically by cable and brake Plastic silos should be sealed immediately after filling to prevent aeration of silage and large dry matter losses (Henderson & McDonald, 1975) Quality of silage stored in plastic silos is proportional to forage density and the extent of anaerobic environment Precautions need to be taken to maintain a tight seal, because 110 JASTER plastic is subject to tears by machinery, animals, or severe weather Plastic is removed or cut, then folded back during feedout It is possible to have cattle self feed silage from plastic bags, but some trampling and wasted feed may result Plastic is not reusable and may pose a disposal problem Bags should be located on a well-drained site, preferably paved to avoid problems when unloading in inclement weather Dry matter losses are close to those found with stave silos, =12 to 13% (Noller & Thomas, 1985) Grass silage stored in a plastic silo bag at 42.9% dry matter resulted in total DM losses of9.0% (Rony et al., 1984) Round bale silage packaging systems are popular because of their labor efficiency (Nicholson et al 1991; Fenlon et al., 1989; Harpster et al., 1985) Harpster et al (1985) outlined the advantages of round bale silage: (i) allows use of hay-making equipment to harvest silage; (ii) does not require silo structures; (iii) can be used to save a mowed field of hay when an anticipated rain storm or extremely high humidity interfere with proper hay curing; (iv) harvesting wilted forage at 50 to 60% moisture reduces leaf loss during baling; since complete field drying is not required, baling time is more predictable; (v) saves about onethird of the harvesting energy and saves fuel compared with silage chopping; and (vi) can be self-fed if properly presented, which saves both labor and fuel Round bale silage also has several disadvantages: (i) conditions associated with round bale silages are not optimum for fermentation; (ii) extreme care must be taken to eliminate air leaks and long stems to reduce bale density; (iii) the system requires prompt handling and storage of bales; (iv) machines for lifting and moving heavy, high moisture bales must be available; (v) either individual plastic bags, storage tubes, or plastic sheets to cover group-stacked bales must be purchased; and (vi) plastic is easily damaged and results in forage losses greater than in conventional storages Three common methods using plastic materials to produce round bale silage include individual bags, multiple bales in bags, and plastic sheet Individual bag bale silo systems use various lengths, diameters, and thickness of plastic covering Bales are lifted with a tractor and spear device and lifted into individual plastic bags Bags are stored and tied-off in position Additional plastic can be applied over the top of individual bags Less labor intensive methods have been developed, including the use of machines that wrap the bale in stretch plastic Fenlon et al (1989) found less spoilage (10.2 vs 21.5% ofDM) and lower invisible losses derived from reduction in bale weight during storage (3.3 vs 6.2% of DM) in wrapped bales than in bagged bales Nicholson et al (1991) reported there was a more desirable fermentation pattern in big bales ensiled at 350 to 410 g DM kg-1 than those made at 460 to 510 g DM kg-1 Machinery is available to place several bales in a long plastic tube, which is then sealed at both ends Producers have found plastic tubes to save labor and be effective for preserving round bale forage; however, more bales will spoil if a bag is tom or opened for long periods during feeding Round bales also may be stacked under sheets of plastic during storage Attempts are made to provide airtight seal by covering plastic ends with soil or sand Problems exist with this system of storage because of the potential for air leaks spoiling a large number of bales LEGUME AND GRASS SILAGE PRESERVATION 111 SUMMARY This article has attempted to outline the principles of silage fermentation of legume and grass forages as well as providing a practical understanding of silage additives and their use to affect silage fermentation While the factors and requirements for fermentation are reasonably well understood, the complex interactions occurring with the addition of microbial inoculants and cell wall degrading enzymes are not well understood Further, the management and environmental interactions on silage fermentation are profound and far from elucidated REFERENCES Anderson, R., H.I Gracey, S.J Kennedy, E.F Unsworth, and R.W.J Steen 1989 Evaluation studies in the development of a commercial bacterial inoculant as an additive for grass silage: I Using pilot-scale tower silos Grass Forage Sci 44:361-369 Apolant, S.M., and D.M Chestnut 1985 The effect of mechanical treatment of silage on intake and production of sheep Anim Prod 40:287-296 Autrey, K.M., T.A McCaskey, and J.A Little 1975 Cellulose digestibility of fibrous materials treated with cellulase J Dairy Sci 58:67-71 Beck, T 1978 The microbiology of silage fennentation p 61-115 In M.E McCullough (ed.) 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Chemistry and biochemistry of herbage Vol 3 Academic... protein degradation during wilting and found no relationship between lengths of wilting and total N or ash content Ammonium formed in the field comes from deamination of amino acids and amides and it is difficult to separate that caused by plant enzymes from that caused by microorganisms Papadopoulos and McKersie (1983) examined protein hydrolysis during wilting and ensiling of alfalfa, red clover... affected very little REFERENCES Albrecht, K.A., W.F Wedin, and D.R Buxton 1987 Cell-wall composition and digestibility of alfalfa stems and leaves Crop Sci 27:735-741 Barlow, E.W.R., R Munns, N.S Scott, and A.H Reisner 1977 Water potential, growth, and polyribosome content of the stressed wheat apex J Exp Bot 28:909-916 Bums, J.C., C.H Noller, and C.L Rhykerd 1964 Influence of method of drying on the... Crop Science Society of Agronomy and American Society of Agronomy, 677 S Segoe Rd., Madison, WI 53711, USA Post-Harvest Physiology and Preservation of Forages CSSA Special Publication no 22 1 2 MOSER walls become highly lignified and nutrients become less available Lower stems may store a considerable amount of nonstructural carbohydrate, but in most perennial grasses and legumes these storage areas... plant and the lamellar system was disrupted The stroma proteins crystallized 2 h after leaf detachment When the tonoplast and plasmodesmata become nonfunctional and cytoplasmic membranes are disrupted, cell components are severely damaged and cells cannot recover with rehydration (Levitt, 1980) Shrinking of cell contents during drying and swelling during rehydration irreversibly damages cell membranes and. .. 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Jaster, E H 1995 Legume and grass silage preservation p 91-115 InK Moore and M.A Peterson (ed.) Post-harvest physiology and preservation of forages CSSA Spec Pub! 22 CSSA and ASA, Madison, WI Jeffers,... quality and quantity These losses are incurred through a complex set of biotic and abiotic processes that occur during harvesting and field operations, and later during storage and handling of... Post-harvest physiology and preservation of forages p 12-20 In Proc Am Forage and Grassl Council, Springfield, IL 2-5 Mar 1987 Am Forage and Grassl Council, Lexington, KY Fitter, A.H., and R.K.M